With the explosion in the growth of Internet usage among both businesses and households, telephone companies have been pressured to provide affordable, high bandwidth access that will support high-speed multimedia services, such as video on demand, high speed Internet access, and video conferencing. To meet this demand, telephone companies are increasingly turning to xDSL technology. The xDSL technology, while having several different embodiments, can provide throughput rates over 100 times faster than that available through traditional 56 kbps modems.
The following are some of the xDSL technologies that are either available today or are currently being tested on a trial basis: Asymmetric Digital Subscriber Line (ADSL), which has a throughput of 32 kbps to 8.192 Mbps downstream to the customer and 32 kbps to 1.088 Mbps upstream to the network; Rate Adaptive Asymmetric Digital Subscriber Line (RADSL), which is a rate adaptive variation of ADSL; High-bit-rate Digital Subscriber Line (HDSL), which offers full duplex throughput at T1 (1.544 Mbps) or E1 (2.048 Mbps) data rates; Symmetric Digital Subscriber Line (SDSL), which provides bi-directional throughput at data rates ranging from 160 Kbps-2.084 Mbps; and Very high-bit-rate Digital Subscriber Line (VDSL), which provides high data rates for customers close to the central office (e.g., 51 Mbps for subscribers within 1000 feet). But most importantly, xDSL technologies offer these high data rates over a standard copper telephone line. Thus, with such a large, embedded copper network already in place, network operators view xDSL technology as a means for extending the life of their investment in copper by many years.
Not all copper telephone line connections, or subscriber loops, between a central office and customer locations, however, are suitable for transmitting xDSL signals. A subscriber loop may, for example, include loading coils that would prevent the successful implementation of xDSL communication. Therefore, it is often necessary to conduct pre-qualification tests to identify potential communication impairments and to determine the likelihood that a DSL modem, if installed at a certain subscriber premises, will perform according to the proposed service offering. Furthermore, once a DSL modem is installed at a customer premises, qualification tests and in-service tests are often used to determine existing communication impairments and to compare DSL modem performance against the proposed service offering.
Subscriber loop testing is very important to DSL service providers, especially for the purpose of qualifying and provisioning a loop for DSL operation. The importance of such testing is highlighted by the creation of new companies, such as Turnstone, that specialize in subscriber loop testing. This need for testing may accelerate as the American National Standards Institute (ANSI) Spectrum Management Standard reaches approval, and as Competitive Local Exchange Carriers (CLECs) challenge loop parameter allegations of Incumbent Local Exchange Carriers (ILECs). This testing will be crucial not only at initial installation, but afterward as loop conditions change due to more DSL crosstalk from the ever-increasing number of DSL services. Moreover, as higher performing DSL equipment becomes available, newer tests may be developed for conducting pre-qualification and qualification testing.
Presently, loop testing is segregated into three types: (1) Portable test equipment that a technician applies temporarily to the loop to be tested; (2) permanent, dedicated loop test equipment placed in-line with DSLAMs; and (3) loop test equipment housed inside DSLAMs with test functions switched onto the line to be tested. ILECs also have metallic line testing (MLT) that is restricted to public telecommunication systems (PTS) frequencies. Traditionally, however, each of the above mentioned test equipment only offers a limited number and variety of subscriber loop tests. Therefore, there exists a need for a subscriber loop testing system that is capable of efficiently and effectively performing a greater number and variety of subscriber loop tests.